Resonance chamber structure including vacuum tube electrode components



Jan. 6, 1970 K. FRITZ 3,488,555

RESONANCE CHAMBER STRUCTURE INCLUDING VACUUM TUBE ELECTRODE COMPONENTS 2 Sheets-Sheet.1

Filed April 26', 1967 FIG.

NFIG.3

10% wen/fr Jan. 6, 1970 K. FRITZ 3,488,5

RESONANCBCHAMBER STRUCTURE INGLUDING'VACUUM TUBE ELECTRODE COMPONENTS Filed April 26, 19 2 Sheets-Sheet 3 FIG.5

Fl 6.? I

FIG.70

IN VEN TOR. MFA f/P/rz 3,488,555 RESONANCE CHAMBERSTRUCTURE INCLUDING VACUUM TUBE ELECTRODE COMPONENTS Karl Fritz, 26 Wendelstn, 6200 Wiesbaden- Dotzheim, Germany Filed Apr. 26, 1967, Ser. No. 634,004 Claims priority, application Germany, Apr. 28, 1966, F 49,052; Aug. 16, 1966, F 50,086; Feb. 21, 1967,

Int. Cl. H01j 19/80, 7/46 US. Cl. 315-39 13 Claims ABSTRACT OF DISCLOSURE The present invention relates to a microwave waveguide and resonance chamber arranged in such a way that it can support electron vacuum tube components, and more particularly to such a tube useful for microwave heating and defrosting and cooking of food.

The frequency ranges permitted for industrial microwave use are so set that interference with communication channels is avoided as much as possible. Wavelengths of from 30 centimeters down to 12 centimeters have been set by the proper licensing authority. The frequency band permitted is very narrow, which requires comparatively expensive microwave generators. The longer wavelength is preferred. With the wavelength of 12 centimeters, the depth of penetration of microwave energy into frozen food on the average is only 2 cm. This means, that larger objects take an appreciable period of time to be thawed out because otherwise the surface burns or chars whereas the interior remains frozen.

Frequencies of 30 to 40 cm. have the advantage that the radiating energy' has a greater depth of penetration. Thisresults in even and rapid thawing, or cooking, as required by modern kitchens, and as desirable for private household use. Such longer wavelengths require an enclosed spaced which is completely wave tight since leakage radiation is required to be extremely small and, on the average, not exceed watt.

The'generators for microwaves in customary'use at the present time are usually magnetrons. Magnetrons are particularly suitable for such use because it is a simple, massive construction, entirely of metal, which can readily be incorporated within the resonance circuit of the entire assembly. The magnetron thus can, together with its coupling system, form a simple unitary structure, which can readily be replaced and adjusted even by unskilled personnel, since installation of the magnetron in a microwave oven is then only a mechanical assembly. Unfortunately, however, the magnetron requires comparatively powerful current supply, and auxiliary equipment which substantially increases the first cost. Additionally, the size and weight of a magnetron, in comparison with a grid controlled vacuum tube, is large.

Grid controlled vacuum tubes have the advantage of being simpler and more reliable; however, the associated resonance circuits are complicated. Known grid controlled microwave tubes do not have the output power of magnetrons and thus have to be used in combination with an 3,488,555 Patented Jan. 6, 1970 external resonance circuit. Such microwave tubes, as known, are constructed in steps or in parallel disc form. The high frequency electrode connections are then discs of cylinders consisting of Kovar (27% Ni, 19% C0, remainder Fe) or fernico (28% Ni, 19% Co, 0.3% Mn, 0.1% C, remainder Fe) with a covering coating of a noble metal. The electrode contacts are sealed 01f by a vacuum seal made of glass or ceramic. The outer resonance circuits are then connected to the electrodes by means of contact springs. These contact springs often do not make good electrical contact with the vacuum tubes and high losses occur at the point of connection, sufficiently high at times to cause contact failure. The non-unitary assembly of the resonance circuit is further of disadvantage in installing and in adjusting the grid controlled tube.

vIt is an object of the present invention to provide a unitary microwave resonance chamber constructed in such a way that it can also function as a grid controlled vacuum tube, so it has the advantage of the unitary structure of the magnetron with the operating advantages of a grid controlled tube.

SUBJECT MATTER OF THE INVENTION Briefly, in accordance with the present invention, the unitary microwave resonance chamber and electron tube assembly comprises a tubular metalsleeve which has a metallic grid structure extending transversely thereto; anode and cathode structures are located on either side of the grid, so that a pair of resonance chambers are defined on either sidethereof. The anode and cathode structures are electrically separated from the sleeve forming the grid by means of insulating rings, such as ceramic rings, sealed to the sleeve in a vacuum tight manner. Thus, a pair of wave-guide resonance chambers are formed, providing a pair of resonance circuits combined with built-in vacuum tube elements. Coupling of energy, into or out of the tube, is done over the di-electric rings between the metal cylinders, that is'the outer sleeve and the anode or cathode electrodes; or over windows cut into the outer sleeves in the region of the dielectric rings, or there beyond. The metallic cylinders forming the electrodes are closed off to the outside by other metal rings, insulated from the sleeves forming the electrodes, which outer cylinders can be slidably (and iilsulatingly) slipped over the tube. Bysliding the outer cylinders or sleeves with respect to the tube components, the resonance chambers can be tuned.

The structure, organization and operation of the invention will now be described more specifically in the following detailed description with reference to the accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view of the resonance chamber, with vacuum tube components, in accordance with the present invention;

FIGURE 1a is a perspective detail view of the cathode structure;

FIGURE 2 is a partial sectional view with a coupling waveguide;

FIGURE 3 is a partial sectional view with a coupling window;

FIGURE 4 is a cross-sectional view of the tube in combination with a coupling waveguide;

FIGURE 5 is a cross-sectional view, in schematic form, of a modified tube in accordance with the invention, capable of wide frequency adjustment;

FIGURE 6 is a longitudinal, schematic view in accordance with another embodiment of the invention;

FIGURE 6a is a partial enlarged view of the end construction of the tube of FIGURE 6;

FIGURE 7 is a longitudinal view of another embodiment of the invention; and

FIGURE 7a is a partial cross-sectional end view of the assembly of FIGURE 7 to an enlarged scale.

Referring now to the drawings and more particularly to FIGURE 1: a metal sleeve 1 forms the outer covering for the resonance chamber wave-guide vacuum tube assembly. Its inner surface is connected to a grid disc 23. The grid disc, electrically connected to sleeve 1, separates the space beneath the grid cylinder or tube sleeves into a pair of chambers; a cathode cylinder 2 is arranged in one chamber, co-axially with the outer sleeve 1. An anode cylinder 3 is arranged in the other chamber, likewise coaxially with the sleeve 1. The pair of inner cylinders 2, 3 are again metallic and extend from the ends of the sleeve until just almost to the grid disc 23, so that the chambers defined by the sleeve, by the grid disc, and by the inner cylinders 2, 3 formcavity resonators with the cathode and anode cylinders as the inner conductors.

The anode cylinder 3 is a solid piece of metal, having a central bore 4 therein, in order to permit insertion of a liquid or a gas cooling head, not particularly shown, and standard in the art. The massive anode 3 merges, at its outer end, with a cylindrical neck piece 24. The neck piece 24 and sleeve 1 are separated from each other by a ceramic insulating ring 9. It is sealed to the two metal parts 24, and 1 respectively to form a vacuum tight insulation shield and at the same time electrically separate the anode and the grid cylinders. The anode neck is bulged outwardly, as seen at 5, which simultaneously permits an equalization of mechanical stresses and further shields ring 9 from electron bombardment due to stray electrons from cathode 2. Preferably, the outer diameter of the anode cylinder and of the bulge 24 is dimensioned with respect to the inner diameter of the grid cylinder 1 in such a manner that the major portion of the reactive energy in the resonance circuit is reflected at the bulge 5, so that all parts located therebeyond are electrically unstressed, so that the electrical energy passing beyond bulge 5 is only that which is necessary to tune the resonance chamber.

Cathode cylinder 2 is formed similar to the anode cylinder, and is also'secured to a ring-formed neck portion 25, bulged outwardly similar to the anode neck 24. Beneath the cathode filament or heat supply is a radiation shield 6. Filament connection 7 is conducted through the cathode neck 25 in insulated relation. It can be formed unitary with an exhaust tip, as shown at 8. A ceramic insulating ring 9 separates the cathode assembly 2 and the grid cylinder or sleeve 1, and closes the grid-cathode resonating chamber in vacuum tight sealed relation while simultaneously separating cathode cylinder 2 from the grid cylinder electrically.

The dielectric insulating rings 9, 9' form, together with the electrode walls, a ring condenser. It can, also be considered to be a low resistance cavity wave guide having a dielectric therein. These cavity guides are so dimensioned that just sufficient energy can pass therethrough which is necessary for tuning of the grid-cathode circuit, and to couple the control energy thereto. On the other hand, coupling of the output can be obtained thereover; as well as tuning of the grid-anode circuit. In a preferred form, the output is coupled from a window 19 of the anodering condenser (or, looked at in a different way, the anode waveguide) as will be described in detail below (see FIG- URE 3).

A thin dielectric foil consisting of a low-loss, high dielectric strength material such as polytetrafiuorethylene surrounds the anode or cathode cylinder at its terminal end and separates the anode or cathode cylinders 24, 25 from a metallic ring 11 having a U-shaped cross section. The plastic layer or foil 10 is preferably coated with a low-loss lubricant in order to suppress glow or corona discharges. Ring 11 is both rotatable, and axially moveable, with respect to sleeve 1, over the dielectric foil 10 and forms the termination of the resonance circuit, that is the ring-form hollow conductor between the grid cylin der and the anode or cathode cylinder respectively. In order to provide for accurate adjustment, outer sleeve 1 is formed with threads 12 which match threads or inturned edges on sleeve 11. Rotating sleeve 11 then adjusts the longitudinal position of sleeve 11 with respect to the sleeve 1. Of course, high frequencies are coupled through the thin foil 10, so that sleeve 11 acts as a terminal short circuit for the resonance chamber waveguide. A cylindrical handle or manipulating sleeve 13, shown only at the cathode end, may be placed over sleeve 11 which can be knurled in order to increase'ease of manipulation.

Wiih respect to high frequency, the microwave resonance chamber-vacuum tube combination is thus completely closed. For purposes of direct current supply, the three electrodes, that is grid 23 and its sleeve 1, anode 3, and cathode 2 are insulated from each other by ceramic rings 9. The entire structure thus is essentially like a waveguide resonance chamber, arranged in such manner that the internal parts can function as vacuum tube elements. The entire arrangement, as shown in FIGURE 1, is preferably operated as a grounded grid amplifier. I

Grid disc 23 is formed with Openings 21 (FIGURE Id) at the outer edge thereof, which function as feedback openings and which can be suitably dimensioned for selfoscillation. The neck of the cathode tube 2 is likewise formed with short staggered slits 22 which decrease heat radiation towards the outside. These slits are shielded internally of the cathode assembly by means of shield 26. The inductance of the resonance chamber is hardly changed by these slits, because each high frequency circuit path around one slit has associated therewith another circuit path, around an opposite slit, and in the opposite direction, so that a homogeneous distributed by-filarity condition obtains at the slits at the circumference of the cathode structure 2. The shielding cylinder 26, in the interior of the cathode cylinder 2 not only acts as a heat shield, but further shields penetration of high frequency energy towards the interior of the cathode structure.

FIGURE 2 illustrates coupling of the microwave energy to a rectangular waveguide 16, having a narrow wall 17 and a wide wall 18. The anode cylinder is elongated, from its juncture with the neck 24, as seen at 3', and extends towards the opposite wall 18 of waveguide 16. The length of the anode cylinder, that is the position of the waveguide 16 with respect to the sleeve 1 is suitably arranged in accordance with the wavelength to be used. Wall 18'itself has a bulge 18 formed therein, which again is suitably dimensioned in accordance with the wavelength desired, to afiford maximum coupling from anode extension 3'. Cooling of the anode is schematically indicated only by the two cooling inlet tubes 15. The space between the extension 18' of waveguide 16 and anode extension'3 may be filled with dielectric material, with lossy material, or may include matching and tuning stubs or short circuit elements, not shown, and well known in the art.

FIGURE 3 illustrates coupling of output energy over a window 19 directly from the anode space. Window 19 is arranged above the dielectric ring 9 in the sleeve 1; the ring 9 is visible at 20. As has been mentioned above, the dielectric of ring 9 at the same time seals the chambers from outside air and to hold the vacuum therein, while electrical insulating the anode and the cathode structures. Any ceramic vacuum type seal is suitable. The window is then so dimensioned in order to leave a sufficient surface on sleeve 1 to be sealed against the ceramic. Its size, its actual position and its length is determined by the match-- ing requirements and the wavelength. A superposed slider, or a foil underlay which can be pulled from beneath the window can vary its size; alternative constructions to vary the size of the window will readily suggest themselves.

FIGURE 4 illustrates coupling of the resonance cham" her having a window, directly to a waveguide, or a utilization chamber, in which the polarization direction of the microwave energy supplied into the chamber is considered.

Rotation of the entire tube assembly with respect to an outer holding strap 16 can vary the exposure of the window 19 to the utilization space or waveguide coupled thereto.

Ordinarily, theresonance chambers of the structure of the present invention are tuned to the base frequency, that is )\/4. Any larger capacity can be coupled out by shortening the electrode shaft, or shortening the hollow .ring conductor. The dielectric within the hollow conductor is placed at a point of smallest electrical field. It is desirably of highest electrical quality and a good conductor of heat; a suitable material is pure aluminum oxide, A1 9 The electrical field at the point of location of the dielectric is so small that the frequency shift caused by the dielectric can be neglected. For a tube of 1,000 nil-12., and a power of about 1 kw., the length of the shafts ajtj the side of the grid cathode is about 16 mm.; and at the grid-anode about 34 mm. 2

So far, one form of microwave tube has been described which has a comparatively small band width, and a comparatively small tuning range over the frequency band of design. The tuning enabled by this form of the invention is essentially that which compensates for variations during manufacture. Referring now to FIGURE 5, an embodiment of the invention is shown in which 'the resonance chamber-Vacuumtube combination can be tuned over a frequency band which is wide enough to cover n/4 where n is larger or equal to 1. In this form of the invention, the grid sleeve 1 and the cathode and anode cylinders 2 and 3 are extended over and beyond ceramic rings 33, 33 in accordance with the wavelength desired. The transition through the vacuum chambers can be done without any substantial change in wave resistance of the waveguide or any abrupt fvariation at the point of the location of the ceramic. Asf'seen in FIGURE 5, the presence of the insulating disc 33, causing cross capacity, can be compensated by change of the diameter of the concentric conductors. By decreasing the diameter of the inner conductor, and increasing the diameter of the outer conductor, additional inductivity is' created which compensates for the cross capacity due ta the dielectric. Capacitative short circuit discs 34 are then placed at suitable points in the extending electrode cylinders which are slideable to tune the resonance circuits. Coupling of energy to, or from the waveguide-tube combination can then be similar "as illustrated and discussed with respect to FIGURES 2 to 4, above. I

The microwave reasonance chamber-vacuum tube combination discussed up to now contains a single control grid, that is, is designed for use as a triode. FIGURES 6 and 7 illustrate arrangements in which multi-grid tube components can be used in the resonance chambers of the present invention. These further grids can be placed in the cathode chamber or at the anode chamber.

FIGURE 6 illustrates a further grid 27, led to the outside by means of a separate connection 28 formed in sleeve 1. The two grids 23, 27 are separated in the plain of the grids by means of a ceramic flange or ring 29. FIG- URE 6a illustrates a connecting ring, in enlarged view, to interconnect the anode and outer sleeve 1, and having a U-shaped cross-section again to serve as a tuning stub.

FIGURE 7 illustrates a microwave guide and vacuum tube component unit having an additional grid 30, connected to a coaxial sleeve 31 which, at its end points is connected by vacuum tight ceramic rings 9a, 9b with the immediately adjacent waveguide elements. Tuning of the additional grid circuit can be done by means of a U-shaped short circuiting ring (see FIGURE 6a) or by means of a Z-ring, as illustrated at an enlarged scale at FIGURE 7a. The length of the tuning sections, and their relative adjustments, is given by the choice of the wave resistance of the lines.

It is preferred that the resonance chambers, and the waveguides are tuned when the waveguide is assembled, so that the resonance chamber structure according to the present invention having n electrodes requires re-tuning 6 upon installation only of n2 connections. One less tuning step is necessary, that is one tuning step per electrode can be avoided when the tube is already constructed with internally short-circuited (with respect to high frequency current) connections. The Waveguide of the present invention is constructed in such a manner that components thereof can function as vacuum tube .gcomponents, that is, as anodes, cathodes and grids. The invention has been illustrated and described as embodied in a resonance chamber-vacuum tube fcomponent combination structure particularly adapted for industrial applications; it is not intended to be limited to the details shown, and various modifications and structural changes may be made as determined by the requirements of particular applications or uses, without departing from the inventive concept. I claim: 1. Unitary microwave resonance chamber and electron tube structure comprising an evacuated tubular electrically conductive metal sleeve (1); i

a metallic grid structure (23) located in said sleeve transverse to the axis of said sleeve and electrically connected to the inside surface thereof throughout its circumference along central plane transverse to the axis of said sleeve to divide said electricallyconductive sleeve into a pair of resonance chambers on either side of said grid structure (23); i

an anode structure (3) and a cathode structure-(2), said anode and cathode structures being formed by a pair of metallic cylinders each located on a respective side of said grid structure and extending into the chambers within said sleeve, and further providing the inner conductors of said pair of resonance chambers on each side of said grid;

and insulatin g frings (9, 9, 33') located inside of said sleeve securing said cylinders within said sleeve and insulating said cylinders from said sleeve and'sealing said cylinders therein in vacuum tight relation, the cathode, grid and anode structures providing a pair of resonating circuits unitary with vacuum tube elements.

2. The structure of claim 1 wherein said cathode cylinder (2) is a 'hollow, cylindrical structure (FIGURE 1a) having a closed end wall providing a cathode; and circumferentially' extending narrow slots formed in the cylindrical wall; and an inner shielding cylinder (26) located in the interior of said cathode cylinder and shielding said slots from escaping radiation, said slots decreas' ing the radiatioii of heat in the radial direction without substantial change in the inductive impedance of the cylinder.

3. Structure as claimed in claim 1 wherein said insulating rings are ceramic rings bonded to and electrically, butair-tightly separating said sleeves and said cylinders, said rings being positioned between said sleeve and said cylinder at a distance from said grid structure at minimum electrical fields, said resonance chambers defined by said grid and by said cathode and anode structures, respectively, being dimensioned to be M4, where A is the wavelength of the microwave oscillations.

4. Structure as claimed in claim 3 including a closed metal cylinder, each, coupled to, but direct current isolated from and in sliding insulating engagement with said cylinders and extending therefrom to tune the resonance chambers.

5. Structure as claimed in claim 1 includes a pair of closed cylindrical tuning structures (11), each formed as closed metal cylinders having an outer wall portion and a re-entrant portion, said re-entrant portions being insulated (10) from, but electrically coupled to said cathode (2) and anode (3) structure respectively, and said outer portions being coupled to said sleeve (1), each said cylindrical structures (11) being slidable with respect to said sleeve and said cathode, and anode cylinders, respectively to tune the resonance chambers.

6. Structure as claimed in claim 6 wherein a thin plastic foil (10) is interposed between said pair of closed cylindrical structures (11) and said anode (3), and cathode (2) structures respectively to provide for DC isolation, but for high frequency electrical coupling.

7. Structure as claimed in claim 6, wherein at least one of said closed cylindrical structures is formed with a circumferential window to couple output energy from the respective resonance chamber to a utilization device.

8. Structure as claimed in claim 7 wherein said window is arranged in the region of the respective insulating ring (9) the output energy being coupled through said insulating ring to provide for vacuum tight connection of said resonance chamber to a utilization device while providing for direct electrical coupling of energy to said utilization device.

9. Structure as claimed in claim 1 including an additional sleeve structure arranged concentric with, and insulated from, said tubular metal sleeve; additional grid means arranged in said additional sleeve structure; and

insulating rings interposed between said sleeve structures and said cathode and anode structures separating in insulated, vacuum tight relation, said chambers.

10. Structure as claimed in claim 9 including coupling means contacting said sleeve structures beyond the insulating rings, said coupling means being slidable thereon to provide for tuning of said resonance chamber.

11. Structure as claimed in c1aim.1 including additional grid means arranged in said sleeve, and spaced from said anode and cathode structures, respectively; a means forming electrical connections from said additionalgride means, said electrical connection means pass ing through said sleeve.

12.,In a microwave resonance chamber structure, an outer tubular conductor (1);

grid means (23)' located transverse to the axis of said tubular conductor intermediate the length thereof;

a pair of inner, cylindrical conductors (2, 3), one each located directly within said tubular conductor at one side of said grid means (23),

ceramic rings sealing said inner cylindrical conductors and said outer tubular conductor together in coaxial insulated, vacuum tight relation, said cylindrical conductors Within said tubular conductor defining a pair of resonance chambers separated from each other by said grid means;

one of said inner cylindrical conductors being emissive to form a cathode (2) and the other being heat dissipative to form an anode (3);

and means coupling microwave energy from said resonance structure to a utilization device.

13. Structure as claimed in claim 12 including metal sleeves in microwave frequency coupled relationship with said outer tubular conductor and said inner conductors, respectively, while electrically insulated from one of said conductors, to provide for tuning of said resonance chamber structures.

References Cited UNITED STATES PATENTS 2,434,115 1/ 1948 McArthur 331-98 X 2,633,537 3/1953 Rambo 331-98 2,994,042 7/ 1961 Power et al. 331-98 3,368,163 2/1968 Douglass 33 l98 FOREIGN PATENTS 902,486 12/1944 France.

HERMAN KARL SAALBACH, Primary Examiner S. CHATMON, JR., Assistant Examiner US. Cl. X.R. 33 177, 78 

